For loop (rarely used in Ruby) - Mini Project: Build & Apply

For loop (rarely used in Ruby)

📖 Scenario: You are helping a small bookstore organize its inventory. The store wants to list the names of some popular books it has in stock.

🎯 Goal: You will create a list of book titles, set up a counter for counting books, use a for loop to go through each book, and finally print each book's name.

📋 What You'll Learn

Create an array called books with the exact titles: 'The Hobbit', '1984', 'Pride and Prejudice'

Create a variable called count and set it to 0

Use a for loop with the variable book to iterate over books

Inside the loop, increment count by 1

Inside the loop, print the current book

After the loop, print the total number of books using count

💡 Why This Matters

🌍 Real World

Bookstores and libraries often need to list and count books in their inventory. Using loops helps automate this task.

💼 Career

Knowing how to loop through lists and count items is a basic skill for many programming jobs, including data processing and software development.

1

Create the list of books

Create an array called books with these exact titles: 'The Hobbit', '1984', 'Pride and Prejudice'

Ruby

# Create the array books with the given titles
# Your code here

Hint

Use square brackets [] to create an array and separate items with commas.

2

Set up a counter

Create a variable called count and set it to 0

Ruby

books = ['The Hobbit', '1984', 'Pride and Prejudice']
# Create a variable count and set it to 0
# Your code here

Hint

Just write count = 0 to start counting from zero.

3

Use a for loop to go through each book

Use a for loop with the variable book to iterate over books. Inside the loop, increase count by 1 and print the current book

Ruby

books = ['The Hobbit', '1984', 'Pride and Prejudice']
count = 0
# Use a for loop with book to go through books
# Inside the loop, add 1 to count and print book
# Your code here

Hint

Use for book in books to start the loop, count += 1 to add one, and puts book to print.

4

Print the total number of books

After the loop, print the total number of books using count with puts

Ruby

books = ['The Hobbit', '1984', 'Pride and Prejudice']
count = 0
for book in books
  count += 1
  puts book
end
# Print the total count of books
# Your code here

Hint

Use puts "Total books: #{count}" to show the total count.

Practice

1. What does the following Ruby for loop do?

for i in 1..3
puts i
end

easy

A. Prints numbers 1, 2, and 3 each on a new line

B. Prints numbers 1 to 2 only

C. Prints numbers 0 to 3

D. Causes a syntax error

Solution

1. Step 1: Understand the range 1..3

   The range 1..3 includes the numbers 1, 2, and 3.

2. Step 2: Loop through each number and print

   The loop prints each number on its own line using puts.

3. Final Answer:

   Prints numbers 1, 2, and 3 each on a new line -> Option A

4. Quick Check:

   for loop with 1..3 prints 1, 2, 3 [OK]

Hint: Remember 1..3 includes 3, so loop prints 1, 2, 3 [OK]

Common Mistakes:

• Thinking 1..3 excludes 3
• Confusing puts with print
• Expecting syntax error

2. Which of the following is the correct syntax for a for loop in Ruby to iterate over an array ["a", "b", "c"]?

easy

A. for x to ["a", "b", "c"] puts x end

B. for (x : ["a", "b", "c"]) puts x end

C. for x in ["a", "b", "c"] do puts x end

D. for x in ["a", "b", "c"] puts x

Solution

1. Step 1: Check the correct Ruby for loop syntax

   Ruby uses for variable in collection do ... end or without do.

2. Step 2: Validate each option

   for x in ["a", "b", "c"] do puts x end uses correct syntax with for x in array do ... end. for (x : ["a", "b", "c"]) puts x end and C use invalid syntax. for x in ["a", "b", "c"] puts x misses end to close the loop.

3. Final Answer:

   for x in ["a", "b", "c"] do puts x end -> Option C

4. Quick Check:

   Correct Ruby for loop uses 'for x in collection do ... end' [OK]

Hint: Remember: for x in collection do ... end is correct Ruby syntax [OK]

Common Mistakes:

• Using colon or 'to' instead of 'in'
• Omitting the 'end' keyword
• Adding parentheses incorrectly

3. What is the output of this Ruby code?

sum = 0
for i in 1..4
sum += i
end
puts sum

medium

A. Error

B. 9

C. 0

D. 10

Solution

1. Step 1: Understand the loop range and sum initialization

   The loop runs from 1 to 4, and sum starts at 0.

2. Step 2: Calculate sum after each iteration

   sum = 0+1=1, then 1+2=3, then 3+3=6, then 6+4=10.

3. Final Answer:

   10 -> Option D

4. Quick Check:

   Sum of 1 to 4 is 10 [OK]

Hint: Add numbers 1 through 4 to get 10 quickly [OK]

Common Mistakes:

• Forgetting to include last number 4
• Starting sum at 1 instead of 0
• Syntax errors in loop

4. Identify the error in this Ruby for loop:

for i in 1..3
puts i


medium

A. Wrong range syntax

B. Missing end to close the loop

C. Variable i not defined

D. Using puts inside loop is invalid

Solution

1. Step 1: Check loop syntax completeness

   The loop starts with for but does not have a matching end.

2. Step 2: Confirm other parts are correct

   The range 1..3 and variable i are valid, and puts is allowed inside loops.

3. Final Answer:

   Missing end to close the loop -> Option B

4. Quick Check:

   Every for loop needs an 'end' [OK]

Hint: Always close for loops with 'end' [OK]

Common Mistakes:

• Forgetting 'end' keyword
• Thinking variable must be declared first
• Believing puts is invalid inside loops

5. You want to create a Ruby for loop that prints only even numbers from 2 to 10 inclusive. Which code snippet achieves this correctly?

hard

A. for i in 2..10 do
puts i if i % 2 == 0
end

B. for i in 2..10 do
puts i if i % 2 == 1
end

C. for i in 1..10 do
puts i if i % 2 == 1
end

D. for i in 2..10
puts i
end

Solution

1. Step 1: Identify the range and condition for even numbers

   The range 2..10 includes numbers 2 through 10. Even numbers satisfy i % 2 == 0.

2. Step 2: Check each option's condition

   for i in 2..10 do puts i if i % 2 == 0 end prints numbers in 2..10 only if even. for i in 2..10 do puts i if i % 2 == 1 end prints odd numbers. for i in 1..10 do puts i if i % 2 == 1 end prints odd numbers 1,3,5,7,9. for i in 2..10 puts i end prints all numbers without filtering.

3. Final Answer:

   for i in 2..10 do puts i if i % 2 == 0 end -> Option A

4. Quick Check:

   Filter with 'if i % 2 == 0' inside for loop [OK]

Hint: Use 'if i % 2 == 0' inside for loop to print evens [OK]

Common Mistakes:

• Using wrong modulo condition for even numbers
• Not filtering numbers inside loop
• Starting range at 1 instead of 2